Sanders was against most parts of the crime bill, but he had to make concessions because it included provisions to protect women and ban assault rifles.
he said this about the bill:
So in true garbage centrist policymaking (where you try and appease both sides, even though we all know one side is inherently draconian), Clinton threw in a legitimately beneficial policy (Violence Against Women Act, Assault Rifles Ban) into his garbage bill. In retrospect Sanders should have been against it, but it let it be known that it was too punitive and he vehemently opposed the incarcerial parts of the bill. So even though I understand why he signed it, he shouldn't have signed it because, overall, it was a terrible bill for literally one segment of the population.